First of all, there was nothing inaccurate about my post. They are bog-standard CDVs from the 19th century worth a buck or so each.
To make this more stamp related - they don't have stamps on them. Some CDVs do have revenue stamps on them. The fact that they don't means that they weren't from the period from 1864-1866 when they were required.
For more than you might ever want to know about the Sun Tax, see: http://web.newsguy.com/bruceb/london/exhibit01.htm